In general, machine tools refer to machines used for the purpose of machining metallic or non-metallic workpieces into desired shapes and desired dimensions by means of various types of tools by using various cutting or non-cutting methods.
Machine tools are basically classified into turning centers and machining centers according to their machining method. In this case, turning centers machine workpieces by rotating the workpieces, and machining centers machine workpieces by rotating tools.
Such a machining center is a composite machine tool into which a boring machine, a milling machine, and a drilling machine are integrated in a composite manner and which can perform all types of machining, such as cutting, drilling, tapping, etc. This machining center can perform three-axis machining by rectilinearly transferring a spindle configured to rotate a tool in three-axis directions.
Recently, with the development of the automobile, shipbuilding and aircraft industries, parts having complex shapes have increased in number. To improve the productivity of the machining of such parts, five-axis machining apparatuses capable of five-axis machining are widely used instead of a method of performing partial machining by means of a plurality of machining centers which perform three-axis machining. In this case, two-axis machining added to conventional three-axis machining may include rotating-axis machining adapted to rotate a table supporting a workpiece and tilting-axis machining adapted to tilt a spindle.
In this case, the plane of tilting movement in which the spindle is tilted needs to form a right angle with the plane of movement formed by rectilinear axes parallel to the table supporting a workpiece, i.e., a transverse rectilinear axis and a lateral rectilinear axis.
Meanwhile, in a structure in which a tilting head configured to tiltably support a spindle is connected to the transfer shaft of a transfer unit configured to transfer the spindle in a vertical direction in an integrated manner and reciprocates rectilinearly in a vertical direction, the inconvenience of also adjusting the transfer shaft in the vertical direction occurs during the process of adjusting a location so that the plane of the tilting movement of the spindle forms a right angle with the plane of the movement formed by the above-described transverse rectilinear axis and lateral rectilinear axis.
In other words, to adjust the plane of the tilting movement of the spindle, the fastening states of a ball screw and a nut used as the transfer shaft in the vertical direction need to be adjusted separately or the ball screw needs to be re-installed, it is necessary to check whether the plane of the tilting movement forms a right angle while moving the transfer shaft in the vertical direction, and it is necessary to repeatedly adjust the plane of the tilting movement of the spindle, the ball screw, and the nut when a right angle is not formed.
As described above, the conventional five-axis machining apparatus has a problem in that lots of time and effort are required to adjust the plane of the tilting movement of a spindle.
Furthermore, a five-axis machining apparatus needs to perform various types of cutting, including heavy cutting and high-speed cutting, on workpieces in order to machine complex shapes and various materials.
However, as the size of a spindle increases, it becomes more difficult to stably tilt the spindle, and thus there is a limitation on the size of the tiltable spindle.
Furthermore, due to the limitation on the size, when a built-in motor type spindle in which a drive motor is provided inside a spindle is used, it is difficult to implement the high-speed, low-torque and low-speed, high-torque rotation power which is required for a five-axis machining apparatus.
Therefore, it is necessary to provide a drive motor outside a spindle and rotate the spindle, in which case a problem arises in that it is not easy to supply rotation power to the tiltable spindle from the outside.